Lorenzo Tabacchini wrote (2013-10-17 09:30:17 +0200):

Hi, is there an easy way to transform a function from: Monad m => a -> m b to: Monad m => m (a -> b)

No, because there are some functions of type a -> m b which cannot be expressed as m (a -> b), consider for instance the function safeRecip :: Double -> Maybe Double safeRecip 0 = Nothing safeRecip x = Just $ recip x You can't turn that function into Maybe (Double -> Double) without losing information about what happens to 0. What do you want to do ? Such "functions" of type m (a -> b) are used in the more general case of Applicative functors to generalize fmap to functions with more than one argument. Consider a function g :: a -> b -> c Let's assume you got a Functor f, then you can use fmap to make fmap g :: f a -> f (b -> c). With a Functor, you can't go much further without nesting f's, but with an Applicative, you have (<*>) :: Applicative f => f (a -> b) -> f a -> f b Control.Applicative also defines (<$>) = fmap, so you can make a function fmap2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c fmap2 g a b = g <$> a <*> b This is exactly Control.Applicative.liftA2 (or Control.Monad.liftM2). -- Olivier